Grinding



June 25, 1935. J. DESENBERG 2,005,718

GRINDING Filed Oct. 26, 1951 r41; 42' 40 v z a E [7a Z7 1 10.!!! [262Ll.

Patented June 25, 1935 UNITED STATES GRINDING Josef Desenberg, Cologne,Germany Application October 26, 1931, Serial No. 571,188 In GermanyOctober 28, 1930 13 Claims.

with loose grinding-surfaces working on universal joints and whichsurfaces by means of their ball-sockets are carried along in irregularmovement through contact with the rotating opposed surface, it wasadmittedly impossible in actual practice to maintain distinct relativemotions of both working surfaces inasmuch as the contact was constantlyvarying and, among other things, depended also upon the ever-changingconsistency of the grinding grains, on the actual oscillating movementitself, on the size and quality of the effective contact-surface, on thefric-- tion-coefiicients, and other factors.

In the type of machine now under consideration, the axis of rotation ofthe grinders and lens-holders is maintained without the use of universaljoints and these lines cut one another in or near the optical centre ofcurvature, with complete and unvarying surface-contact of both grinderand lens-holder, which results in the grinding movements shown in Figs.1 and 2. By reason of their comparatively unfavorable grinding orpolishing effect, this type of machine was generally speaking onlysuitable for particular operations, such as the manufacture of bi-focallenses etc.

The working methods now to be described attempt to secure considerablybetter grinding and polishing ellects in such lens-grinding machineswhose axis of rotation cuts the optical centre of curvature by means ofsystematically controlled relative point lines (i. e. the mark made bythe individual grinding grains on the lens and on the grinding surfaceby wet grinding medium, or the mark made on the lens when a hardgrinding medium is used. I The designation is also used in reference tothe mathematical direction taken by the grinding grain, apart from thetrack it makes on the glass).

In particular, it has been proved to be specially advantageous insecuring the quickest result when grinding and smoothing (in some casesalso when pre-polishing) to do the work in as short a space of time aspossible by choosing the right speed of rotation with the result that avery large number of hard (ceramically burnt) or soft (wet) grindinggrains are brought into operation.

To secure more accurate results when finally polishing (in some casesalso when pre-polishing, smoothing etc) it is in many cases advantageouseither to shorten the point-lines on the grinder or systematically so toaffect the said pointlines on the grinder (which not only revolves onits spindle but can move backwards and forwards or alter its speed orreverse its direction or be changed for a large tool producing othereffects) so that the machine in questionwhen working over one or severallenses can vary the point lines during the process by the means abovereferred to. By this means the work is more quickly and moreeconomically executed and a greater accuracy in shaping is attained.

The grinding grains are thus mainly distributed over such lines which(lines) never appear as intersecting curves both on the lens and on thegrinder simultaneously inasmuch as the speed etc of the lens and grinderdo not co-incide. The method of executing the work is such that incoarse or fine grinding (also smoothing or pre-polishing) firstly onemakes very short grinding strokes on the lens and then when finallypolishing (or smoothing or pre-polishing) either short polishing strokeson the grinder or by oscillation etc special spiral or oscillatory curvestrokes.

The procedure to effect comparatively-short point lines simultaneouslyupon the lens and upon the grinder can also be effected by giving agreater angular velocity (and thereby the main action) to the smallerlens surface on its rotating spindle while using the largergrinder-surface with less angular velocity (and thereby subsidiaryaction) in conjunction. The effect of this difference in the action ofgrinder and lens creates definite (and comparatively short) spiral pointlines on the lens-surface. Transferring the main work to-the lens hasthe advantage of making quicker and more precise workmanship.

At the same time, in many cases it will be suflicient or necessary, inorder to secure intersecting point-lines when grinding or polishing, forexample, to alter the relative rotary speed or direction of rotation ofthe spindle in the process, or to select difierent sizes of grinder ofuniform average diameter, or grinders of different widths.

For this purpose in order to facilitate the change of grinders on oneand the same toolspindle, one can arrange the various grinding andpolishing tools in concentric form separate from one another. Thus anautomatically consecutive grinding and polishing service is considerablyfacilitated. And the inaccuracies caused by dismounting the lens andengaging it with another spindle are completely avoided. The change oftools can be, for example, so efiected that the grinders which work ina. group together (concentric, mutually interacting) are mounted on spines so arranged that various grinders come into ction automatically oneafter another (by means of a capstan or such like). i

The highest possible number of grinding or polishing grains are broughtinto play, which in spite of concentric surfaces, impinge from withoutonthe lens material (a result impossible if the grains only remain betweenthe two surfaces and do not impinge from without). Therefore thepressure of the two surfaces on one another can be reduced. In practicethis renders possible, better working speed and a greater quantity of Imaterial cut away by the grinding process. Inasmuch as the various pointlines are intentionally altered during the grinding process, the exactgrinding of the lenses is more completely attained. The whole result isthat the process is considerably accelerated and a speedy automaticmanufacture is rendered possible, as has been proved in practice.

This influence and the already mentioned facts connected with it have uptill now not received sufficient attention. Therefore there has been noattempt, by suitable choice of relative rotary speed or other pertinentdetails, to shorten the point-lines on the principal working surfaces,to vary the choice of grinding and polishing strokes, as well as thetime to which the direction and radial curves of the grinding andpolishing strokes can be set in a particularly favomable conjunction.

Figure I is a diagrammatic view showing the outline of a lens and by acurved line the point path of a grinding grain over the face of thelens.

Figure II is similar to Figure I but showing a relatively long pointpath with numerous intersections.

Figure III is a central sectional detail view, partly broken away, of agrinding device adapted to carry out my invention.

Figure IV is a detail central sectional view of a modified form ofdevice showing two grinding tools and their holders.

Figure V is a detail central sectional view of a further modified deviceshowing a lens, polisher and the supporting means therefor and FiguresVI, VII and VIII are views similar to Figures I and II but showing pointpaths of different forms.

In general, when grinding and polishing, one chooses the point-linesillustrated in Figs. II and I, which in the main give infinitely longand frequently intersecting curves.

In the following examples, the process will be discussed and developedin greater detail by reference to schematic design.

In Fig. III the lens is fastened on the holder 2 which is supported bythe hollow rotating spindle 3. The spindle 3 is mounted on twoballbearings 4 and 5 which are mounted in the casting 6' and areadjusted with this to an invisible vertical axisdirection throughspindle 3 to grinder-spindle I (i. e. adjusted to the central point P ofthe working surface) so that the two spindles 3 and I cut at everydesired angle of axis in the optical centre "0 (below or above theworking surface). The tool-spindle I carries on its mandrel-guide 8(with conical head 9) the tool-holder III with the annular grindingtool.

, At the lower end of the tool-holder III a coupling-clutch I2 isprovided, which looks with the opposing teeth of the disc I 3,' so thatthe speed of the tool II is governed by the rotation of the disc I3 onspindle I. The bush' I4, by means of a key governs spindle I and isdriven by its pulley II. Spindle 3 is driven from the pulley I6.

By the process above-described, a spherical seating, with the distanceof the grinding-surface from the axial point of intersection as radius,must be created with mathematical exactitude (even when the shape of theparts originally chosen varies) and must be attributed to the fact thatboth grinding pieces wear themselves away or work themselves down untilcomplete surfacecontact is achieved, which is only rendered possible bythe spherical seating referred to.

A change in. the various grinding and polishing tools for the aboveprocess can be carried out as in Fig. IV which is particularlyapplicable to automatic machines by a mechanical device e. g. the toolholder I 0 is lowered by spindle 1 until the flange-ring I8 rests on thetransport-plate II. A sideways motion of the transport-plate I I is madeand the succeeding tool II' comes into the position left by the tooltaken out of action. The spindle I thus disengages from the teeth I2 ofthe tool I I andengages again when II is above it.

Fig. V is intended to show that the lower grinder II when smoothing orpolishing can remain fixed to its holder III on spindle 1. The

larger hatlike carrier I0 01 the tool II (next to be used) is fixed overthe grinder II and the teeth I2 are engaged in the teeth of the holderI0. Either of these or other following tools can be fitted (whennecessary) with a guard to prevent splashing of grinding grains. The twotools shown in the diagram V do not come simultaneously into contactwith the lens. Either the grinder on the hatlike carrier II or thegrinder II, but not both at once.

Disconnccting, removing, engaging and fastening of. the grinding disc II which is responsible for the grinding accuracy, is not necessary atevery stage of the process nor by altering the course of thegrinding-grains, as can be seen by Fig. V so that a saving is secured inworking methods and precise fixing in the position. The lessening orabsence of interruptions in the work to change tools of variousdegreesor groups of grinding lines when grinding, smoothing, prepolishing orfinally polishing is very advantageous in the application of the aboveprocess with automatic or semi-automatic machines with fixed (notball-jointed) spindles. If necessary, the mounting and dismounting ofthe polishing head II can take place quite automatically withoutstopping the spindles.

Assume the middle diameter of the grinding tool-surface at point P to bed/l, the diameter of the lens to be d/2", the peripheral speed of thegrinder at point P to be u/l and the peripheral speed of the lens tobeu/2, the result, for the outside calculation in the production is acompletely straight grinding-line running through the centre of theworking-surface diametric from circumference to circumference in fiatgrinding-surfaces and gives the mathematical formula d/I a] ma h? Thismathematical comparison is only exact mathematical calculation presentthe rnselves. 'I'o counteract any idea that the grinding lines in Fig.VI only intersect in the middle of the surface of -the lens, it shouldbe pointed out that by an appropriate width of grinding tool a sheaf ofcurves can be secured which in practice provides a sufficientcounteraction. against any undesirable irregularities of surface.

Fig. VII is to illustrate a number of grinding strokes which gothroughthe middle of the surface of the lens or grinder and make shorttransits.

Should the calculatory or pictorial description of the grinding strokesseemto be complicated, it is easy to make them ocularly visible by meansof a small grinding ring with a comparatively coarse grinding grain and,if necessary, with the aid of a magnifying glass.

By changing over from a coarser to a finer grinding or polishing grainof hard or wet nature, especially when going over from the grinding tothe polishing process, which can be done on the same or differentspindles, it will possibly be better to alter the grinding or polishingstrokes where the lens-surface or tool-surface are small. 'Il'iis can bedone quite simply e. g. by changing the relative speed of the rotationor the direction of same, either during the operation or by usingpolishing stones or polishing discs whose diameter or working surfaceare intentionally different in proportion to the last tool used.

In Figs. III and IV the grinding or smoothing tool ll consists of asmall grinding ring. In Fig. V the polishing tool consists of a completepolishing disc or a wide polishing segment. The systematic alteration ofor addition to curve-groups sufiices in every case to provide a speedypreliminary polish or a good final polish in the working-method underconsideration.

This is especially the case if the coarse and fine grinding (orsmoothing) is executed in the already mentioned manner with shortstrokes on the lens, the pre-polishing or final-polishing (or smoothing)with short strokes or with spiral or oscillatory curve-strokes on theworking-surface of the lens.

Fig. VIII is to illustrate a spiral point-line, which goes through themiddle of the surface of the lens and makes comparatively short transit.

By systematic movement (by a grinding tool, composite lever-system,model, etc) by the lensspindle 3 in Fig. 111 e. g. by oscillating orswing-- factured by short grinding strokes whereby in case .of necessity(e. g. by irregular lenses) special carrier joints can be used.

As the grinding machines now under consideration have not onlysuflicient exactness for single-piece methods and also quicker polishingpower, but have also a better centering and maintenance of the middlethickness of the glass etc. over the usual machines and methods withsocalled multiple-polishing and multiple-grinding (group of lenses) afurther noteworthy effect of the said process is that the machine underconsideration now renders practically possible a very advantageousautomatic or semi-automatic grinding or polishing system withsingle-piece (one lens) with a small and comparatively simple machine.

In consequence of the former use of grinding and polishing strokes withsmall power, it is useless under such conditions to use the machineslast referred to for spherical and arpherical lenses from large to smalldiameters in massproduction such as is the pre-condition for anautomatic system.

By means of the process now under consideration one can work on severallenses fixed in the usual manner to the same holder and using hard orwet grinding or polishing grains comparatively quickly with greatworking speed at one and the same time in multiple-grinding ormultiple-polishing by means of one spindle whereby the total workingsurface is made up of several separate surfaces.

Though only one lens is fastened to the rapidly rotating spindle 3,nevertheless a number of such single-lens spindles can work to a quicklymoving concave, flat or convex grinder H, as can be seen in the dotteddiagram (see Fig. III, left corner).

In case it appears advantageous, to secure a quicker machine-setting orwhen using outsidelimit or calliper' device for the axial tool-movement,to maintain the position of the grinding surface (point P) in one place,one can regulate the lens-holder 2 (which can, if necessary, be givenvarying lengths or axial variability for varying lens-curves) by avariable axis going through P as indicated in Fig. 111.

This is then especially suitable when using hard or wet grinding orpolishing grains with the usual automatic device in metal-working with acapstan-machine combining it effectively with the above-describedprocess.

It is known that principally 'by the glassgrinding machines withuniversal-jointed lensholders and so-called rocking motion,comparatively favourable polishing results have been obtained,especially by flat or slightly curved surfaces on largepolishing-machines or grindingmachines where very many lenses aremounted together on a common holder which is made as large as possible.

But if one looks closer at the surface of single pieces done by thispopular multiple method, one sees faults caused by the uncontrollableand constantly changing grinding; and, in general, the length andcurvature of the strokes have grown in proportion to the above-mentionedincrease of the grinding surface. The mounting of the glasses next toone another causes many difliculties (in regard to opticalcentralization, maintenance of a particular middle thickness, equalityof polishing and grinding of all the lenses, safe mounting andunmounting, apart from freedom from scratches on the lenses themselves)and is by the nature of the case with sharply curved lenses unable to becarried out at all or only in a limited form.

The widely used coarse grinding process, generally adopted bymetal-polishers with limited demands on exactness or fineness of surface(whereby the machine grinds forward step by step in relatively slowprogress with very poor line-control and imperfect surface-contact) isnot practicable for brittle optical glasses for various reasons althoughthe grinding strokes admittedly show no deviations, or very few, and arevery short.

It will be understood in the accompanying claims where I use thewordgrinding without reference to polishing, I use the word in a genericsense including polishing.

